The present invention concerns improved lubricating oils such as those useful for gasoline engines of the type that are lubricated by mixing the oil with the fuel that is fed to the engine. Ordinarily this lubricating procedure is employed for gasoline engines having a 2-stroke cycle, for example, outboard motors for powering various types of boats. In particular it is concerned with lubricating oils for such 2-stroke gasoline engines containing Mannich base additives made from alkyl phenols, aldehydes and amines.
Usually when lubricating a 2-stroke-cycle gasoline engine, the lubricating oil is mixed with the fuel to the engine in a ratio of 1 volume of lubricant to form about 20 to 80 volumes of fuel. The mixture first enters the crankcase where the mixture of lubricant and unvaporized fuel contacts and lubricates the various moving surfaces including the bearings, pistons, piston rings and cylinders. All of the lubricant that does not deposit on the surfaces in the lower part of the engine passes into the combustion chamber where it is burned along with the fuel. The amount of lubricant that thus reaches the combustion chamber is much greater than the amount of lubricant that is normally burned in an automotive-type gasoline engine, i.e., a 4-stroke engine employing a crankcase and crankcase oil. Because of this, combustion-chamber-deposit-induced problems (e.g., ring sticking and preignition) are prevalent. These result in power loss, runaway preignition and sometimes piston failure can occur. Power loss due to spark plug fouling from combustion chamber deposits is usually the first performance limitation encountered.
High temperatures resulting from preignition or other causes (e.g., cooling failures, improperly lean mixtures, ignition system malfunctioning), can lead to insufficient lubrication near the exhaust ports, excessive wear, scuffing, scoring, and even seizure.
There has been an increased need for a lubricating oil composition that will be more suitable than conventional motor oils for 2-stroke-cycle engines, particularly for outboard motor service. Certain makes of engines are more critical than others. In general, modern high horsepower (i.e., above 25 horsepower, and particularly above 40 horsepower) outboard motors produce more piston, ring zone and cylinder deposits than do lower horsepower models. Severe plug fouling and preignition conditions are presented by full throttle operation with highly leaded fuel (2 to 3 ml. per gallon) and ash containing lubricants.
A high performance, 2-stroke-cycle engine lubricant should be readily miscible with gasolines and should (1) provide good lubrication (low friction, low wear, and no deformation, scuffing, scoring or seizing) of the rubbing parts such as antifriction bearings, piston rings and cylinders; (2) maintain a clean combustion chamber with attendant long spark plug life and freedom from preignition; and (3) control deposits.
Compounding a lubricant to maximize all of these benefits in all applications of 2-stroke engines (of the type fueled and lubricated by a mixture of gasoline and oil) is not a simple matter of adding conventional crankcase lubricating oil ingredients with known functions, because of interaction effects. That is, conventional lube oil additives, employed for their known beneficial properties, can also have detrimental effects. Thus, some detergents can keep the piston clean, but at the expense of poor lubrications, lower spark plug life and more preignition. These interaction effects require a very specially compounded lubricant to minimize operating troubles and to maximize performance and life.
A commercially available ashless two cycle oil additive package comprises an amide-imide prepared by reacting isostearic acid with a polyethylene amine believed to be essentially tetraethylene pentamine in a mol ratio of 3 moles of acid to one mole of amine (see U.S. Pat. No. 3,100,673) with mineral oil as the diluent. Additive package treats for 2-stroke-cycle gasoline engines, particularly the high performance water cooled engines used in boating, ranges from 8.25-9.75 volume percent of additive.
Mannich bases as engine oil additives are well known and have been widely reported in the patent literature, e.g, U.S. Pat. Nos. 2,348,638; 2,353,491; 2,459,112; 2,459,113; 2,459,114; 2,459,115; 2,459,116; 2,723,907, and 3,036,003.
These additives which are particularly effective for engine oils are based upon condensation products of hydroxyaromatic, an aldehyde and an amine. These additives are often multifunctional in character, acting as antioxidants, dispersants and as pour depressants therein. These compounds have also been recognized as exhibiting detergent properties. Hydroxyaromatic compounds which are substituted by a short chain alkyl group or by a relatively high molecular weight straight chain aliphatic hydrocarbon derived from chlorinated wax such as wax phenols, referred to in U.S. Pat. No. 2,459,114, are also suitable.
A class of alkyl hydroxybenzyl substituted polyamines closely related to those of the present invention is that resulting from the reaction of from 0.5 to 2 moles each of C.sub.4 to C.sub.20 alkyl phenol and formaldehyde for each basic nitrogen in an alkylene polyamine. The alkylene polyamines usually used are the di-, tri- and tetra-ethylene, tri-, tetra and pentamines. The resulting products, illustrated in U.S. Pat. No. 3,036,003, include some disclosed to be useful per se in lubricant oil formations as ashless-type detergents.
U.S. Pat. No. 3,539,633 teaches that dispersant-detergent-antioxidant hydroxy-alkylbenzyl substituted alkylene polyamines are obtained from C.sub.50 and higher carbon content alkylphenols reacted with formaldehyde and alkylene polyamines with the molar ratios are 1.0-1.5:1.5-2.0:1.0-1.5, respectively. The aforementioned hydroxy (C.sub.50 and higher) alkylbenzyl substituted alkylene polyamines are also useful as lubricant additive compounds when reacted with a boron compound which forms a coordinate boron complex with polar groups present.
In none of the foregoing patents is there any teaching that other than about an equimolar amounts of the hydroxy aromatic (phenolic) compound and the aldehyde should be employed in the Mannich reaction when the molar ratio of the aromatic to amine is about 2 to 1. None of these publications relating to Mannich bases suggest that the bases would be useful as a detergent-antiscuff additive for lubricants useful in 2-stroke cycle gasoline engines; particularly large water cooled engines, e.g., the 130 horsepower outboard.